1. Field of the Invention
The present invention relates to a method for scrubbing an amine-type extractant, and in more detail, the present invention relates to a method for scrubbing an amine-type extractant, which is capable of efficiently removing a chloro complex ion of a metal, in regeneration of the amine-type extractant supporting the chloro complex ion of a metal such as iron, zinc, which easily accumulates in the amine-type extractant, in a scrubbing stage constituting a solvent extraction step, as well as capable of regenerating extraction ability of the extractant so that it can be repeatedly reused as it is in an extraction stage of the solvent extraction step. It should be noted that the solvent extraction step here includes an extraction stage for supporting the chloro complex ion of a target metal contained in an aqueous solution of a raw material onto the extractant, by the amine-type extractant constituting an organic phase, and a subsequent reversed extraction stage for eliminating of a target metal, which is supported on the extractant of the organic phase, by an aqueous solution forming a water phase, and subsequently a scrubbing stage for separating and removing components remaining in the organic phase from the organic phase by an elimination or substitution reaction, by the aqueous solution forming the water phase.
2. Description of the Prior Art
In a hydrometallurgy of non-ferrous metal, various methods, where valuable metals are leached from ores or other raw materials and they are separated and purified from the resulting leaching solution, are carried out. For Example, in a hydrometallurgy of nickel, it is important technical element to separate nickel and cobalt contained in an aqueous solution of an acidic chloride, and in general, there are used an oxidative neutralization method utilizing the fact that cobalt is more easily oxidized than nickel, or an solvent extraction method with various organic extractants. Among these, the oxidative neutralization method has a problem that a reprocessing step of once separated cobalt precipitate is required separately in order to sufficiently separate cobalt, because high amount of nickel is co-precipitated in generating cobalt precipitate, and thus it could not be said a desirable method in the case where cobalt concentration in an aqueous solution of nickel is high.
On the other hand, in the solvent extraction method for separating nickel and cobalt, an organic extractant to be used is classified into a phosphate ester-type acidic extractant represented by CYANEX 272, and an amine-type extractant represented by TNOA (Tri-n-octylamine), TIOA (Tri-i-octylamine) or the like, and both types have excellent separation performance of cobalt and nickel. However, in general, in the case of an aqueous solution of a chloride with high concentration of a metal ion and a chloride ion in the solution, the amine-type extractant is used. These reasons include that the amine-type extractant has more excellent separation coefficient of cobalt and nickel as compared with the acidic extractant, in an aqueous solution under the above condition, due to formation of a cobalt chloro complex ion; and cost of the acidic extractant requiring a neutralization agent in extraction operation is high; and its operation without generation of clad is difficult. It should be noted that “clad” is one forming a third phase, wherein the fine particular insoluble residue flown-in during the solvent extraction step, or generated in the solvent extraction step gather at an interface between an organic phase and a water phase, together with solvent deteriorated products and the like, which raises a serious problem in view of production efficiency.
By the way, in solvent extraction operation, the amine-type extractant has the following characteristics.
The amine-type extractant usually becomes to have sufficient extraction characteristics, by the addition of hydrochloric acid according to the following reaction formula 1, and shows excellent separation characteristics of cobalt and nickel, because extraction of a chloro complex ion is carried out according to the following reaction formula 2:R3N:+HCl═R3N:H+Cl−  [Formula 1]
By this reaction, an amine (R3N:) generates an amine added with hydrochloric acid by hydrochloric acid.R3N:H+Cl−+MCl3−═R3N: H+MCl3−+C−  [Formula 2](wherein, M represents metal species, which form a chloro complex ion such as Zn, Fe, Cu, Co.)
According to this reaction, metal species, which form a chloro complex ion such as Zn, Fe, Cu, Co, are extracted to form an amine supporting a metal chloro complex ion. It should be noted that because nickel does not form a chloro complex ion, it is left in an extraction residual liquid and separated. Therefore, in the case where metals having higher formation capability of a chloro complex ion than cobalt, that is, more strongly supported metals, for example, chloro complex ion such as iron, zinc, is contained in a nickel aqueous solution, these metals are also extracted.
By the way, in a reversed extraction stage of cobalt from the amine-type extractant supporting the above metal chloro complex ion, cobalt is easily eliminated in the aqueous solution by bringing the extractant into contact with a weakly acidic aqueous solution. However, a chloro complex ion of a metal such as iron, zinc, which is more strongly supported than cobalt, is not eliminated so easily as cobalt. Therefore, in the case where the amine-type extractant is reused repeatedly in a solvent extraction step, iron, zinc or the like results in to be accumulated gradually in an extractant. Accordingly, supporting of cobalt onto the amine-type extractant in the extraction stage is interfered, and finally results in significant reduction of extraction of cobalt. As a method for solving this, there is installed a scrubbing stage for separating and removing these metals from the amine-type extractant supporting a chloro complex ion of a metal such as iron, zinc.
For Example, in the scrubbing stage, by bringing the amine-type extractant supporting a chloro complex ion of a metal such as iron, zinc, into contact with an aqueous solution not containing a chloride ion, and by reducing a chloride ion down to concentration to dissolve the chloro complex ion contained in the amine-type extractant, it is possible to separate and remove these metals, however, in order to attain this, a large quantity of scrubbing solution is required and thus not practical. Therefore, as other method, there has been proposed a method for removing a chloro complex ion accumulated in an extractant, by bringing it into contact with a strong alkali aqueous solution in a scrubbing stage, so as to be neutralized (for Example, refer to Patent Literature 1). It should be noted that in such a method by alkali neutralization, in general, by bringing an alkali solution of sodium hydroxide or the like into contact with the extractant, according to the following reaction formula 3, a metal chloro complex ion is removed as a hydroxide.R3N:H+MCl3−+3NaOH═R3N:+3NaCl+H2O+M(OH)2   [Formula 3](wherein M represents metal species, which form a chloro complex ion such as Zn, Fe.)
In this case, iron is removed as hydroxide precipitate, or zinc is removed as hydroxide precipitate or a hydroxo complex ion, from the extractant, however, because it is a reaction accompanying precipitate formation, and filtering of the extractant composed of an organic solvent, along with the solution, is required, it was a troublesome work. In addition, because sodium hydroxide is expensive as an operation material, and thus not desirable to use in removing iron and zinc having small recovery merit, and still more the amine-type extractant itself returns to a free amine state by the above alkali neutralization, there was a problem that the addition of hydrochloric acid or sulfuric acid is required afterwards, in order to completely regenerate extraction capability thereof.
Still more, as other method, there has been proposed a method for hydrochlorination of an amine, in the scrubbing stage, by bringing the amine-type extractant supporting a chloro complex ion of a metal such as iron, zinc, into contact with an aqueous solution containing any of a sulfuric acid ion, a nitric acid ion, a phosphoric acid ion, and substantially not containing a chloride ion, to eliminate these metals, and then by bringing the eliminated amine-type extractant into contact with a solution containing a chloride ion (for Example, refer to Patent Literature 2), however, it requires a multiple times of scrubbing by using a fresh water phase to obtain sufficient reversed extraction ratio of zinc or the like, by only contact with a water phase composed of such an aqueous solution, which results in increased amount of a scrubbing solution.
Under these circumstances, it has been required a more efficient method for scrubbing, which is capable of attaining no accompanying of precipitate and clad formation, low cost of an operation material, and reduced amount of a scrubbing solution, in regeneration of extraction capability of an amine-type extractant supporting a chloro complex ion of a metal such as iron, zinc, in a scrubbing stage constituting a solvent extraction step.
Patent Literature 1: JP-B-06-043620 (page 1)
Patent Literature 2: JP No. 3844752 (pages 1 and 2)